This invention relates in general to construction materials for a wide variety of uses, as, for example, in repairing cracks, holes and dents in the hulls and bodies of boats and land vehicles, leaks in gas and liquid conduits such as exhaust pipes and water pipes, and leaks in gas and liquid tanks and other containers; repairing fractured poles, booms, spars, antennas, and the like, and strengthening similar structures that are not fractured; patching roofs, gutters, and drainpipes; sealing leaking containers of pressurized fluids, such as air-conditioning systems, swimming pools, and hydraulic hoses; and electrically insulating all manner of articles. More particularly, the invention provides construction materials for the foregoing and other purposes comprising a flexible web impregnated with a pliable mastic in a sealed package which maintains its contents in stable soft and pliable conditions until opened, after which the web is applied to the use intended and the mastic begins to harden in place upon exposure to water, or to only the moisture in the air. The mastic is able to harden and cure under water, salt or fresh.